Clean ups

[miasma]

I've analyzed the code with IntelliJ's inspections and applied a couple of common refactorings.

• redundant overrides add bloat and don't have any functional effect
• redundant variable is used as return value and can be inlined
• redundant label does not improve readability when there is only one label
• nested classes with static operate more efficiently
• method references are potentially more efficient and more readable than anonymous classes
• refactored API calls document the intent better (and can be used since the pom.xml defaults to jdk11)
• redundant imports slow down build process